Avoid failing HTTP/2 requests with upgrade-insecure-requests (#12799)

Motivation:
This is a non-standard header that is not _explicitly_ called out as connection related, even though it can be argued that it is.
Regardless, Chrome and Firefox do actually send this header in their HTTP/2 requests, so rejecting these is quite troublesome.
Safari doesn't send this header.

Modification:
Remove the check for `upgrade-insecure-requests` in the header validation in HpackDecoder.
Also update tests to match.

Result:
HTTP/2 requests from Chrome and Firefox are no longer rejected by the header validation.

Fixes #12798

codec-http2/src/main/java/io/netty/handler/codec/http2/HpackDecoder.java

@@ -422,13 +422,12 @@ private static HeaderType validate(int streamId, CharSequence name,
 
     @SuppressWarnings("deprecation") // We need to check for deprecated headers as well.
     private static boolean isConnectionHeader(CharSequence name) {
-        // These are the known standard and non-standard connection related headers:
+        // These are the known standard connection related headers:
         // - upgrade (7 chars)
         // - connection (10 chars)
         // - keep-alive (10 chars)
         // - proxy-connection (16 chars)
         // - transfer-encoding (17 chars)
-        // - upgrade-insecure-requests (25 chars)
         //
         // We scan for these based on the length, then double-check any matching name.
         int len = name.length();
@@ -449,7 +448,7 @@ private static boolean isConnectionHeader(CharSequence name) {
         if (len == 16) {
             return contentEqualsIgnoreCase(name, HttpHeaderNames.PROXY_CONNECTION);
         }
-        return len == 25 && contentEqualsIgnoreCase(name, HttpHeaderNames.UPGRADE_INSECURE_REQUESTS);
+        return false;
     }
 
     private static boolean contains(Http2Headers headers, CharSequence name) {

codec-http2/src/test/java/io/netty/handler/codec/http2/DefaultHttp2HeadersDecoderTest.java

@@ -167,9 +167,6 @@ public void decodingConnectionRelatedHeadersMustFailValidation() throws Exceptio
 
         // Non-standard connection related headers:
         verifyValidationFails(decoder, encode(b(":method"), b("GET"), b("proxy-connection"), b("keep-alive")));
-        verifyValidationFails(decoder, encode(b(":method"), b("GET"), b("upgrade-insecure-requests"), b("1")));
-        verifyValidationFails(decoder, encode(b(":method"), b("GET"),
-                b("content-security-policy"), b("upgrade-insecure-requests"), b("upgrade-insecure-requests"), b("1")));
 
         // Only "trailers" is allowed for the TE header:
         verifyValidationFails(decoder, encode(b(":method"), b("GET"), b("te"), b("compress")));